Optical member, optical system using the optical member, and method of manufacturing an optical member

ABSTRACT

Provided is an optical member capable of keeping a high performance antireflection effect over a long period of time with respect to an arbitrary substrate. The optical member has plural layers on a substrate, and includes at least one metal oxide layer having a void, and at least one layer containing an organic resin as a main component formed between the substrate and the metal oxide layer. The metal oxide layer is a plate crystal layer formed of a plate crystal containing aluminum oxide as a main component and a surface of the plate crystal layer has an uneven profile. The organic resin has an aromatic ring and/or a hetero ring in at least a part thereof.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 12/544,264filed Aug. 20, 2009, U.S. Pat. No. 8,163,333 B2, which is a continuationof application Ser. No. 12/180,987 filed Jul. 28, 2008, U.S. Pat. No.7,771,832 B2, which is a continuation of International Application No.PCT/JP2008/053129 filed Feb. 19, 2008, which claims the benefit ofJapanese Patent Applications No. 2007-040003 filed Feb. 20, 2007, andNo. 2008-033290 filed Feb. 14, 2008.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optical member having anantireflection property and an optical system using the same, and moreparticularly, to an optical member suitable for obtaining a highantireflection property in a visible region to a near infrared regionover a long period of time, and an optical system using the same.

2. Description of the Related Art

It is known that an antireflection structure using a fine periodicstructure having a wavelength of the visible light region or a shorterwavelength forms a fine periodic structure having an appropriate pitchand height, and thereby shows an excellent antireflection property in awide wavelength region. As a method for forming a fine periodicstructure, coating of a film in which fine particles having a particlediameter equal to or less than the wavelength are dispersed (JapanesePatent No. 03,135,944) or the like is known.

Further, it is known that a method of forming a fine periodic structureby formation of a pattern by a finely processing apparatus (electronbeam lithography apparatus, laser interference light exposure apparatus,semiconductor light exposure apparatus, etching apparatus, etc.) allowsa pitch and a height to be controlled, and enables the formation of thefine periodic structure having an excellent antireflection property(Japanese Patent Application Laid-Open No. S50-70040).

As methods other than the methods described above, methods of growingboehmite that is an oxide hydroxide of aluminum on a substrate to obtainan antireflection effect are known. In those methods, a layer ofaluminum oxide (alumina) formed by the vacuum film formation process(Japanese Patent Publication No. S61-48124) or the liquid phase process(sol-gel process) (Japanese Patent Application Laid-Open No. H09-202649)is subjected to water vapor treatment or hot water dipping treatment toform a surface layer into boehmite to form a fine periodic structure,and thereby an antireflection film is obtained.

Further, an antireflection film in which a film which contains SiO₂ as amain component and has a refractive index between that of a substrateand that of boehmite is provided between the substrate and the boehmitehas been proposed (Japanese Patent Application Laid-Open No.2006-259711).

SUMMARY OF THE INVENTION

A metal oxide and a metal halide layer to be formed by a technologyusing fine particles or a method of growing boehmite on a substrate isproduced easily with a high productivity and exhibits excellent opticalcharacteristics. On the other hand, such a metal oxide and a metalhalide layer have a low density and a number of voids, so moisture orthe like reaches the substrate easily from outside, which easily causesthe erosion of the substrate and the elution of a substrate componentsuch as alkali ions. Further, there is a problem in that the elutedcomponent makes it difficult to keep the fine structure, resulting indecreased performance.

Further, in an antireflection film including a film containing SiO₂ as amain component between a substrate and boehmite, a film component iseluted from the film containing SiOn₂ as a main component due to hotwater treatment, which changes optical characteristics.

There is a demand for an antireflection film using a fine periodicstructure, which can be formed more easily and has high reliability inlow-temperature sintering.

The present invention has been made in view of the related art describedabove, and an object is to provide an optical member which can maintaina high-performance antireflection effect over a long period of time forany substrate, an optical system using the same and a method ofmanufacturing an optical member.

The present invention provides an optical member configured in a mannerdescribed below for achieving the above-mentioned object.

The present invention provides an optical member having plural layersformed on a substrate, including at least one plate crystal layer formedof a plate crystal containing aluminum oxide as a main component, and atleast one layer containing an organic resin as a main component formedbetween the substrate and the plate crystal layer, the organic resinincluding an aromatic ring and/or an imide ring in a main chain.

Further, the present invention provides the optical member, in which theplate crystal is boehmite.

Further, the present invention provides the optical member, in which theplate crystal layer has a refractive index that continuously increasesfrom a surface layer side to a substrate side.

Further, the present invention provides the optical member, in which asurface of the plate crystal layer has an uneven profile.

Further, the present invention provides the optical member, in which apercentage of water absorption of the organic resin is 0.05% or more and2% or less.

Further, the present invention provides the optical member, in which theorganic resin is a thermoplastic resin.

Further, the present invention provides the optical member, in which atleast a part of the organic resin has a repeating unit (—SiR₂—O—)_(m),where R is a methyl group or a phenyl group, and m is an integer of 1 ormore and 6 or less.

Further, the present invention provides the optical member, in which therefractive index nb of the substrate, the refractive index ni of thelayer containing the organic resin as a main component, and therefractive index ns of the plate crystal layer formed of a plate crystalcontaining the aluminum oxide as a main component satisfy nb≧ni≧ns.

Further, the present invention provides the optical member, in which thethickness of the layer containing the organic resin as a main componentis 10 nm or more and 150 nm or less.

Further, the present invention provides the optical member, in which thesubstrate is made of glass.

Further, the present invention provides an optical system including theoptical member according to any one of the above-described ones.

Further, the present invention provides a method of manufacturing anoptical member, including: forming a layer containing an organic resinas a main component on a substrate; forming a layer containing aluminumoxide as a main component; and subjecting the layer containing aluminumoxide as a main component to hot water treatment to form unevenness on asurface, characterized in that the refractive index nb of the substrate,the refractive index ni of the layer containing an organic resin as amain component, and the refractive index ns of the layer containingaluminum oxide as a main component satisfy nb≧ni≧ns.

According to the present invention, an optical member capable ofexhibiting a high antireflection effect stably over a long period oftime can be provided.

Further, according to the present invention, an optical system havingthe above optical member can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram illustrating one embodiment of an opticaltransparent element of the present invention.

FIG. 2 is a schematic diagram illustrating one embodiment of arefractive index profile of an optical transparent element of thepresent invention.

FIGS. 3A and 3B are each a schematic diagram illustrating one embodimentof an optical transparent element of the present invention.

FIG. 4 is a photograph in Example 1 (magnification: ×100,000)illustrating a result of observation of a thin film formed on a glasssubstrate and having fine unevenness on the surface from the top surfaceby an FE-SEM.

FIG. 5 is a photograph in Example 1 (magnification: ×150,000)illustrating a result of observation of the cross-section of a thin filmformed on a glass substrate and having fine unevenness by an FE-SEM.

FIG. 6 is a front view of Example 16 of the present invention.

FIG. 7 is a cross-sectional view of Example 16 of the present invention.

FIG. 8 is a front view of Example 17 of the present invention.

FIG. 9 is a cross-sectional view of Example 17, of the presentinvention.

FIG. 10 is a front view of Example 18 of the present invention.

FIG. 11 is a cross-sectional view of Example 18 of the presentinvention.

FIG. 12 is a front view of Example 19 of the present invention.

FIG. 13 is a cross-sectional view of Example 19 of the presentinvention.

FIG. 14 is a front view of Example 20 of the present invention.

FIG. 15 is a cross-sectional view of Example 21 of the presentinvention.

FIG. 16 is a cross-sectional view of Example 22 of the presentinvention.

FIG. 17 is a cross-sectional view of Example 23 of the presentinvention.

DESCRIPTION OF THE EMBODIMENTS

Hereinafter, the present invention will be described.

FIG. 1 is a schematic cross-sectional view schematically illustrating anoptical member according to the embodiment of the present invention. Asshown in FIG. 1, in the optical member of the present invention, alaminated structure including a layer 26 containing an organic resin asa main component and a plate crystal layer 27 formed of a plate crystalcontaining aluminum oxide as a main component formed on the surface ofthe layer 26 is formed on the surface of a substrate 25. The platecrystal forming the plate crystal layer 27 that is one layer of thelaminated structure refers to a plate crystal that is deposited andgrows on the surface layer of a film containing aluminum oxide as a maincomponent when the film is soaked in hot water and then the surfacelayer of the aluminum oxide film is subjected to a deflocculating actionor the like.

The plate crystal layer 27 is preferably a layer of which the refractiveindex continuously increases from the surface layer side to thesubstrate side, and a change in the refractive index with respect to thefilm thickness can be represented by a straight line (a) or a curve (b)or (c) as shown in FIG. 2. Due to the continuous increase in therefractive index from the surface layer side to the substrate side, areflectance reduction effect is larger compared with the case where alayer having higher refractive index is laminated subsequently from thesurface layer side.

Further, the refractive index of the plate crystal layer 27 continuouslyincreases from the surface layer side to the substrate side, so it ispreferred that the surface have an uneven profile. FIGS. 3A and 3B areschematic cross-sectional views schematically illustrating an opticalmember according to the embodiment of the present invention in thiscase.

In FIGS. 3A and 3B, the optical member of the present invention has alayer 29 containing an organic resin as a main component and a platecrystal layer 30 formed of a plate crystal containing aluminum oxide asa main component on the substrate 28.

The surface of the plate crystal layer 30 has an uneven profile 31.

The plate crystal layer 30 containing aluminum oxide as a main componentare formed of a crystal containing an oxide or a hydroxide of aluminumor a hydrate thereof as a main component. Especially preferred crystalsare boehmite. By placing these plate crystals, their end portions formfine unevenness 31, and therefore it is preferred that the platecrystals be selectively arranged with a predetermined angle to thesurface of a layer for increasing the height of the fine unevenness andreducing the intervals therebetween. In the present application, anoxide or hydroxide of aluminum, or a hydrate thereof is referred to asaluminum oxide. Further, one or more oxide layers, which containaluminum oxide alone or any of ZrO₂, SiO₂, TiO₂, ZnO, and MgO, and ofwhich the amount of aluminum oxide is 70 mol % or more, may be referredto as a layer containing aluminum oxide as a main component.

A case where the surface of the substrate 28 is a flat surface such asflat plate, a film, or a sheet is shown in FIG. 3A. It is preferred thatthe plate crystal be arranged with respect to the surface layer of thesubstrate with an average angle of an angle θ1, between an inclinationdirection 32 of the plate crystal and the substrate surface, of 45° ormore and 90° or less, and more preferably 60° or more and 90° or less.

Further, a case where the surface of the substrate 28 has atwo-dimensional or three-dimensional curved surface is shown in FIG. 3B.It is preferred that the plate crystal be arranged with respect to thesurface layer of the substrate with an average angle of an angle θ2,between an inclination direction 32 of the plate crystal and thesubstrate surface, of 45° or more and 90° or less, and more preferably60° or more and 90° or less. Note that there may be a case where thevalue of the angles θ1 and θ2 exceeds 90° depending on the gradient ofthe plate crystals. In this case, measurement is conducted so that thevalue is 90° or less.

The thickness of the plate crystal layer 30 is preferably 20 nm or moreand 1,000 nm or less, more preferably 50 nm or more and 1,000 nm orless. If the thickness of the layer forming the unevenness is 20 nm ormore and 1,000 nm or less, an antireflection property owing to a fineuneven configuration is effective, the possibility that the mechanicalstrength of the unevenness is impaired is eliminated and the fine unevenconfiguration becomes advantageous in terms of manufacturing costs. Bysetting the thickness to 50 nm or more and 1,000 nm or less, theantireflection property is further improved, which is more preferred.

The surface density of the fine unevenness of the present invention isalso important, and the corresponding average surface roughness Ra′value obtained by two-dimensional extension of a center line averageroughness is 5 nm or more, more preferably 10 nm or more, still morepreferably 15 nm or more and 100 nm or less, and the surface area ratioSr is 1.1 or more, more preferably 1.15 or more, still more preferably1.2 or more and 3.5 or less.

One method for evaluating an obtained fine uneven structure isobservation of the surface of the fine uneven structure by a scanningprobe microscope, and by the observation, the average surface roughnessRa′ value obtained by two-dimensional extension of the center lineaverage roughness Ra of the film and the surface area ratio Sr aredetermined. Namely, the average surface roughness, Ra′ value (nm), issuch a value that the center line average roughness Ra defined in JIS B0601 is applied to a measurement surface and three-dimensionallyextended, and the Ra′ value is expressed as a “value obtained byaveraging absolute values of deviations from a reference surface to aspecified surface” and given by the following formula (1).

$\begin{matrix}{{Ra}^{\prime} = \left. {\frac{1}{S_{0}}{\int_{Y_{B}}^{Y_{T}}\int_{X_{L}}^{X_{R}}}} \middle| {{F\left( {X,Y} \right)} - {Z_{0}\ {\mathbb{d}_{x}\mathbb{d}_{y}}}} \right.} & (1)\end{matrix}$Ra′: average surface roughness value (nm),S₀: area when the measurement surface is ideally flat,|X_(R)−X_(L)|×|Y_(T)−T_(B)|, F (X, Y): height at a measurement point (X,Y), where X is an X coordinate and Y is a Y coordinate,X_(L) to X_(R): range of X coordinates on the measurement surface,Y_(B) to Y_(T): range of Y coordinates on the measurement surface, andZ₀: average height within the measurement surface.

The surface area ratio Sr is determined by Sr=S/S₀ (S₀: area when themeasurement surface is ideally flat. S: surface area of an actualmeasurement surface). The surface area of an actual measurement surfaceis determined as follows. The measurement surface is divided into minutetriangles consisting of closest three data points (A, B, C), and thenthe area ΔS of each minute triangle is determined using a vectorproduct. ΔS(ΔABC)=[s(s−AB)(s−BC)(s−AC)]0.5 (where AB, BC and AC are thelengths of the sides, and thus s≡0.5(AB+BC+AC)), and the total sum ofthe areas ΔS is a surface area S to be determined. If Ra′ as the surfacedensity of the fine unevenness is 5 nm or more and Sr is 1.1 or more,antireflection owing to the uneven configuration can be realized. If Ra′is 10 nm or more and Sr is 1.15 or more, the antireflection effectbecomes higher than that of the former case. If, Ra′ is 15 nm or moreand Sr is 1.2 or more, the uneven configuration has a performancecapable of enduring practical use. However, if Ra′ is 100 nm or more andSr is 3.5 or more, the effect of scattering by the uneven configurationpredominates over the antireflection effect so that a sufficientantireflection property cannot be obtained.

The plate crystal layer 30 formed of a plate crystal containing aluminumoxide as a main component in the present invention is obtained bycompounding an Al metal alone film or a metal film containing metal Aland one of metal Zn or metal Mg into the layer 29 containing an organicresin as a main component followed by soaking in hot water at 50° C. orhigher or exposure to water vapor. At this time, the uneven profile 31is formed on the surface of the above metal due to hydration,dissolution, and redeposition. The plate crystal layer 30 can also beobtained by forming a layer containing aluminum oxide as a maincomponent on the layer 29 containing an organic resin as a maincomponent, and dissolving or depositing the surface selectively. Theabove layer containing aluminum oxide as a main component can be formedby a known vapor phase method such as CVD or PVD, a liquid phase methodsuch as a sol-gel process, hydrothermal synthesis using an inorganicsalt, or the like. According to the method of providing a plate crystalof aluminum oxide, an amorphous aluminum oxide layer may remain in alower portion of the uneven profile 31 in the plate crystal layer 30.

It is preferred to use a method of treating a gel film with hot water,the gel film being formed by coating a sol-gel coating solutioncontaining aluminum oxide to grow an alumina plate crystal, because auniform antireflection layer can be formed on a substrate with a largearea or on a non-planar substrate.

For a raw material of the gel film obtained from a sol-gel coatingsolution containing aluminum oxide, an Al compound is used, or at leastone of compounds of Zr, Si, Ti, Zn and Mg is used together with the Alcompound. As raw materials of Al₂O₃, ZrO₂, SiO₂, TiO₂, ZnO and MgO,metal alkoxides of the respective metals and salt compounds such aschlorides and nitrates of the respective metals may be used. Metalalkoxides are preferably used in terms of film formability particularlyfor ZrO₂, SiO₂ and TiO₂ raw materials.

Aluminum compounds include, for example, aluminum ethoxide, aluminumisopropoxide, aluminum-n-butoxide, aluminum-sec-butoxide,aluminum-tert-butoxide, aluminum acetylacetnate or oligomers of thesecompounds, aluminum nitrate, aluminum chloride, aluminum acetate,aluminum phosphate, aluminum sulfate, and aluminum hydroxide.

Specific examples of zirconium alkoxides include zirconilumtetramethoxide, zirconium tetraethoxide, zirconium tetra n-propoxide,zirconium tetraisopropoxide, zirconium tetra n-butoxide, and zirconiumtetra-t-butoxide.

For the silicon alkoxide, various kinds of compounds expressed by thegeneral formula Si(OR)₄ may be used. R is the same or different loweralkyl group such as a methyl group, an ethyl group, a propyl group, anisopropyl group, a butyl group, or an isobutyl group.

Titanium alkoxides include, for example, tetramethoxy titanate,tetraethoxy titanate, tetra n-propoxy titanate, tetraisopropoxytitanate, tetra n-butoxy titanate, and tetraisobutoxy titanate.

Zinc compounds include, for example, zinc acetate, zinc chloride, zincnitrate, zinc stearate, zinc oleate, and zinc salicylate, and especiallypreferred are zinc acetate and zinc chloride.

Magnesium compounds include magnesium alkoxides such as magnesiumdimethoxide, magnesium diethoxide, magnesium dipropoxide and magnesiumdibutoxide, magnesium acetylacetate, and magnesium chloride.

Organic solvents, which may be any organic solvents which do not causeraw materials such as the above-mentioned alkoxides to gelate, include:for example, alcohols such as methanol, ethanol, 2-propanol, butanol,ethylene glycol, and ethylene glycol-mono-n-propyl ether; various kindsof aliphatic or alicyclic hydrocarbons such as n-hexane, n-octane,cyclohexane, cyclopentane, and cyclooctane; various kinds of aromatichydrocarbons such as toluene, xylene, and ethyl benzene; various kindsof esters such as ethyl formate, ethyl acetate, n-butyl acetate,ethylene glycol monomethyl ether acetate, ethylene glycol monoethylether acetate, and ethylene glycol monobuthyl ether acetate; variouskinds of ketones such as acetone, methyl ethyl ketone, methyl isobutylketone, and cyclohexanone; various kinds of ethers such as dimethoxyethane, tetrahydrofuran, dioxane, and diisopropyl ether; various kindsof chlorinated hydrocarbons such as chloroform, methylene chloride,carbon tetrachloride, and tetrachloroethane; and aprotic polar solventssuch as N-methylpyrrolidone, dimethyl formamide, dimethyl acetamide, andethylene carbonate. Of the various kinds of solvents described above,alcohols are preferably used in terms of stability of a solution.

If an alkoxide raw material is used, particularly alkoxides of aluminum,zirconium, and titanium are highly reactive to water, and are abruptlyhydrolyzed by addition of moisture in air or water, resulting in opacityand precipitation. Aluminum salt compounds, zinc salt compounds andmagnesium salt compounds are hard to be dissolved in an organic solventalone, and the stability of their solutions is low. For prevention ofsuch a situation, a stabilizer is preferably added to stabilize thesolution.

Stabilizers may include, for example: β-diketone compounds such asacetyl acetone, dipyrobilemethane, trifluoroacetylacetone,hexafluoroacetylacetone, benzoylacetone, and dibenzoylmethane;β-ketoester compounds such as methyl acetoacetate, ethyl acetoacetate,allyl acetoacetate, benzyl acetoacetate, iso-propyl acetoacetate,tert-butyl acetoacetate, iso-butyl acetoacetate, 2-methoxyethylacetoacetate, and 3-keto-n-methyl valeriate; and alkanol amines such asmonoethanol amine, diethanol amine and triethanol amine. The amount ofstabilizer added is preferably about 1 in terms of molar ratio to thealkoxide or salt compound. After the stabilizer is added, a catalyst ispreferably added for the purpose of promoting part of the reaction inorder to form an appropriate precursor. Catalysts may include, forexample, nitric acid, hydrochloric acid, sulfuric acid, phosphoric acid,acetic acid, and ammonia. As a method for forming a film using theabove-described sol-gel coating solution, for example, a known coatingmethod such as a dipping method, a spin coating method, a spray method,a printing method, a flow coating method, and a combination thereof maybe appropriately employed.

After being coated with the above sol-gel coating solution, it ispreferable to conduct heat-treatment in a range of 120° C. or more and230° C. or less. As the temperature of heat treatment is higher, thefilm is likely to become more dense. However, when the temperature ofthe heat treatment exceeds 230° C., the damage such as deformation iscaused in the substrate. The temperature of the heat treatment is morepreferably 150° C. or more and 210° C. or less. The heating time ispreferably 10 minutes or longer, although depending upon the heatingtemperature.

Then, a gel film which had undergone drying or heat treatment isimmersed in hot water, whereby plate crystals containing aluminum oxideas a main component is precipitated to form an unevenness profile of theoutermost surface. By immersion in hot water, the surface layer of thegel film containing aluminum oxide undergoes a deflocculating action orthe like, and some components are eluted, but due to a difference insolubility in hot water between various kinds of hydroxides, platecrystals containing aluminum oxide as a main component are precipitatedon the surface layer of the gel film, and grow. The temperature of hotwater is preferably 40° C. to 100° C. The hot water treatment time isabout 5 minutes to about 24 hours.

For the hot water treatment of a gel film with oxides such as TiO₂,ZrO₂, SiO₂, ZnO and MgO added as different kinds of components to thefilm containing aluminum oxide as a main component, crystallization iscarried out using a difference in solubility in hot water between thecomponents, and therefore unlike the hot water treatment of the singlecomponent film of aluminum oxide, the size of plate crystals can becontrolled over a wide range by changing the composition of inorganiccomponents. As a result, the unevenness profile formed by plate crystalscan be controlled over the wide range. Moreover, if ZnO is used as asubcomponent, coprecipitation with aluminum oxide is possible, andtherefore the refractive index can be controlled over a further widerange. Therefore, an excellent antireflection property is realized.

The organic resin used in the layer 29 containing an organic resin as amain component of the present invention may have a function of adjustingthe refractive index difference between the substrate 28 and the platecrystal layer 30 containing aluminum oxide as a main component, and maybe transparent in a wavelength region of light to be used.

The layer 29 containing an organic resin as a main component of thepresent invention adjusts the refractive index difference between thesubstrate 28 and the plate crystal layer 30 containing aluminum oxide asa main component, thereby contributing to the exhibition of highantireflection property. Therefore, it is desired that the layer 29 havean optimum film thickness and refractive index, and the optimum filmthickness and refractive index are kept stably from the time when thefilm is produced. In the application of the present invention, a layercontaining 80% by weight or more of an organic resin may be referred toas a layer containing an organic resin as a main component.

It is preferred that an organic resin having an aromatic ring and/or animide ring in a main chain be used in the layer containing an organicresin as a main component of the present invention. An example of thearomatic ring or imide ring includes structures represented by thefollowing chemical formulae.

Because an aromatic ring or an imide ring has a planar structure,molecular chains of an organic resin in which these structures areintroduced in a main chain are likely to be aligned parallel to thesubstrate during the formation of a film. Therefore, even in the casewhere the organic resin layer 29 of the present invention having a filmthickness of several 100 nm or less is used, the uniformity of filmthickness and refractive index is high. Further, in that case, solventresistance is excellent, a glass transition temperature is high, heatresistance is excellent, and film thickness and refractive index areunlikely to change.

When an organic resin having no aromatic ring and/or no imide ring in amain chain is used, molecular chains get entangled with each otherrandomly, so a decrease in refractive index probably caused by adecrease in density is observed when the resin is formed into a thinfilm. This also applies to the case where the plate crystal layer 30formed of plate crystal containing aluminum oxide as a main component isproduced from a sol-gel coating solution containing aluminum oxide. Thatis, for the same reasons as those in the above, the dissolution in asolvent contained in a sol-gel coating solution, a change in filmthickness and refractive index due to swelling, deformation duringdrying by heating, decomposition, and coloring are likely to occur.

Further, in order to obtain the plate crystal layer 30 formed of platecrystals containing aluminum oxide as a main component, a gel filmcontaining the aluminum oxide is exposed to water vapor or is soaked inhot water. At this time, it is desired that the change in film thicknessand refractive index of the organic resin layer be minimized. In view offoregoing, it is preferred to use the organic resin layer 29 in whichdissolution and swelling are unlikely to occur with hot water, unlikethe organic resin having an aromatic ring and/or imide ring in a mainchain. Further, the density of the film in the plate crystal layer islow, so moisture or the like from outside passes through the metal oxidelayer easily and reaches the surface of the substrate. At this time, thesurface of the substrate is eroded with moisture or the like, and asubstrate component is eluted to degrade the performance of the opticalmember. The layer 3 or 5 containing an organic resin as a main componentof the present invention is desired to have an effect of blockingmoisture and the like coming from outside via the plate crystal layer.In order to obtain such an effect, it is preferred to use an organicresin having a low percentage of water absorption. Such an organic resinhas a percentage of water absorption of 0.05% or more and 2% or less.When the organic resin has a percentage of water absorption of 2% orless, the organic resin can block moisture coming from outside. Thepercentage of water absorption as used herein refers to the percentageof water absorption of a film left at 23° C. for 24 hours after the filmis formed. On the other hand, in the case of an organic resin having apercentage of water absorption of less than 0.05%, the adherence to thesubstrate is decreased remarkably. Therefore, even if pre-treatment ofthe surface of the substrate is conducted, the organic resin is peeledoff from the substrate during hot water treatment and the like.

Regarding the kind of the organic resin, any of a thermosetting resinand a thermoplastic resin can be used as long as it is an organic resinhaving an aromatic ring and/or an imide ring in a main chain. Examplesof the thermosetting resin include cured products of a compound or anoligomer having one or more reactive or polymerizable substituents, suchas an epoxy group, an oxetanyl group, an episulphide group, a methylolgroup, an isocyanate group, a thioisocynate group, a vinyl ether group,an acryloyl group, a methacryloyl group, and a maleimide group. Even ifone compound or oligomer contains two or more kinds of reactive orpolymerizable substituents, a cured resin obtained by mixing two or morekinds of compounds having different reactive or polymerizablesubstituents or oligomers, followed by curing can be used. Examples ofthe cured resin having an aromatic ring and/or an imide ring in a mainchain include a cured product of bisphenol A epoxy, a cured product ofm-phenylenediisocyanate, and cured products of a methylomelamine resin,a guanamine resin, and a maleimide resin.

In the case of using a cured resin, an initiator and a curing agent canbe used together when the above compound is cured. The initiator ismostly selected from radical, cation, and anion initiators dependingupon the reactivity of a substituent of the above compound. Further, inthe case of heat curing, a thermal decomposition type initiator iswidely used. Examples of the thermal decomposition type initiatorinclude N,N-azobisbutyronitrile as a radical initiator, and pyridiniump-toluenesulfonate as a cation initiator. Further, in the case of heatcuring, an organic acid such as p-toluenesulfonic acid as a cationinitiator and an organic amine such as diazabicycloundecene as an anioninitiator may be mixed in small amounts. In the case of conductingcuring with light such as UV-light, a photosensitive initiator is used.

On the other hand, examples of the thermoplastic resin having anaromatic ring and/or an imide ring in a main chain include aromaticpolyethers such as polyether ketone and polyether sulfone, aromaticpolyesters such as polyethylene terephthalate, aromatic polycarbonate,aromatic polyurethane, aromatic polyurea, aromatic polyamide, andthermoplastic polyimide. Of those, the aromatic polyethers, aromaticpolysulfides, polycarbonate, and thermoplastic polyimides are preferredin terms of heat resistance.

Further, the thermoplastic resin is more preferred since a refractiveindex and a film thickness do not change under baking conditions, andless uncured monomer remains.

Further, in order to enhance the adherence between the substrate 25 andthe layer 29 containing an organic resin as a main component, it ispreferred to use an organic resin containing siloxane structure(—SiR₂—O—)_(m), where R is a methyl group or a phenyl group, and m is aninteger of 1 to 6.

When the adherence between the substrate 25 and the layer 29 isenhanced, film peeing particularly under high temperature and highhumidity, cracks and the like can be suppressed.

In the organic resin containing (—SiR₂—O—)_(m), the repeating unitincluding (—SiR₂—O—)_(m) is preferably 30 mol % or less based on thewhole repeating units. When it is 30 mol % or more, heat resistance isdecreased due to the decrease in glass transition temperature, andwettability with respect to a glass substrate is decreased.

By changing the structure of an organic resin, the refractive index ofthe layer 2 or 5 containing the organic rein as a main component can bechanged. For example, by increasing the number of aromatic ringscontained in the organic resin and the number of hetero rings containedtherein, the refractive index is enhanced. On the other hand, byincreasing an aliphatic chain, an alicyclic structure, the abovesiloxane structure and fluoroalkyl group, etc., transparency isenhanced, and the refractive index is decreased. Among the organicresins having an aromatic ring and/or an imide ring in a main chain,examples of the organic resins whose refractive indices are changedrelatively easily depending on the structure include polyimide, aromaticpolyethers, aromatic polysulfides, and aromatic polycarbonate. Thesepolymers can introduce the above structure into a main chain or a sidechain together with an aromatic ring and an imide ring via a monomer.

Polyimide is synthesized generally by polyaddition reaction anddehydration-condensation reaction between a dianhydride and a diamine.By introducing an aliphatic chain, an alicyclic structure, or afluoroalkyl group into a diamine and/or a dianhydride, a transparentpolyimide in a visible light region is obtained. In particular, by usingdianhydride having an alicyclic structure, and introducing one or aplurality of various kinds of structures such as siloxane structure, analiphatic chain, an alicyclic structure, and an aromatic ring intodiamine, the refractive index can be changed arbitrarily from 1.5 to1.7.

Examples of a dianhydride used for the synthesis of thermoplasticpolyimide include: aromatic acid dianhydrides such as pyromelliticdianhydride, 3,3′-biphthalic anhydride, 3,4′-biphthalic anhydride,3,3′,4,4′-benzophenonetetracarboxylic dianhydride,3,3′,4,4′-diphenylsulfonetetracarboxylic dianhydride,4,4′-(hexafluoroisopropylidene)diphthalic anhydride, and4,4′-oxydiphthalic dianhydride; and aliphatic acid dianhydrides such asmeso-butane-1,2,3,4-tetracarboxylic dianhydride,1,2,3,4-cyclobutanecarboxylic dianhydride,1,2,3,4-cyclopentanetetracarboxylic dianhydride,1,2,4,5-cyclohexanetetracarboxylic dianhydride,bicyclo[2.2.2]octo-7-ene-2,3,5,6-tetracarboxylic dianhydride,bicyclo[2.2.2]octane-2,3,5,6-tetracarboxylic dianhydride,bicyclo[2.2.1]heptane-2,3,5,6-tetracarboxylic dianhydride,5-(2,5-dioxotetrahydrofuryl)-3-methyl-3-cyclohexene-1,2-dicalboxylicanhydride, and4-(2,5-dioxotetrahydrofuran-3-yl)-1,2,3,4-tetrahydronaphthalene-1,2-dicarboxylicanhydride. From the viewpoint of enhancing solubility, coating property,and transparency of polyimide, preferred are3,3′,4,4′-diphenylsulfonetetracarboxylic dianhydride,4,4′-(hexafluoroisopropylidene)diphthalic anhydride,1,2,3,4-cyclobutanecarboxylic dianhydride,bicyclo[2.2.2]octane-2,3,5,6-tetracarboxylic dianhydride,bicyclo[2.2.1]heptane-2,3,5,6-tetracarboxylic dianhydride,5-(2,5-dioxotetrahydrofuryl)-3-methyl-3-cyclohexene-1,2-dicalboxylicanhydride, and4-(2,5-dioxotetrahydrofuran-3-yl)-1,2,3,4-tetrahydronaphthalene-1,2-dicarboxylicanhydride.

Examples of the diamine used for the synthesis of thermoplasticpolyimide include: aromatic diamines such as m-phenylenediamine,p-phenylenediamine, 3,4′-diaminodiphenylmethane,4,4′-diaminodiphenylmethane, 4,4′-diamino-3,3′-dimethyldiphenylmethane,o-tolidine, m-tolidine, 4,4′-diaminobenzophenone,1,1-bis(4-aminophenyl)cyclohexane, 3,4′-diaminodiphenyl ether,4,4′-diaminodiphenyl ether, 1,4-bis(4-aminophenoxy)benzene,1,3-bis(4-aminophenoxy)benzene,2,2-bis[4-(4-aminophenoxy)phenyl]propane,4,4′-bis(4-aminophenoxy)biphenyl, bis[4-(4-aminophenoxy)phenyl]sulfone,4,4′-bis(3-aminophenoxy)biphenyl, bis[4-(4-aminophenoxy)phenyl]sulfone,9,9-bis(4-aminophenyl)fluorene, 2,2-bis(4-aminophenyl)hexafluoropropane,2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane, and2,2′-bis(trifluoromethyl)benzidine; aliphatic diamines such as1,4-diaminobutane, 1,5-diaminopentane, 1,3-cyclohexanediamine,1,4-cyclohexanediamine, 4,4′-methylenebis(cyclohexylamine),4,4′-methylenebis(2-methylcyclohexylamine), and1,4-bis(aminomethyl)cyclohexane; and —SiR₂—O— group-containing diaminessuch as 1,3-bis(3-aminopropyl)tetramethyldisiloxane and1,4-bis(3-aminopropyldimethylsilyl)benzene. From the viewpoint ofadherence with an inorganic substrate such as glass, it is preferred toinclude at least —SiR₂—O— group-containing diamines such as1,3-bis(3-aminopropyl)tetramethyldisiloxane and1,4-bis(3-aminopropyldimethylsilyl)benzene.

The aromatic polyethers are synthesized generally by subjecting abisphenol and an aromatic dihalide to condensation reaction in a solventin the presence of a base such as potassium carbonate. When bisphenol isreplaced by aromatic disulfide, aromatic polysulfide is synthesized. Byintroducing one or a plurality of various kinds of structures intobisphenol or aromatic disulfide and aromatic dihalide, the refractiveindex can be changed arbitrarily from 1.5 to 1.7.

Examples of the bisphenol used for the synthesis of aromatic polyetherinclude resorcinol, hydroquinone, 4,4′-biphenol,2,2-bis(4-hydroxyphenyl)propane, 4,4′-dihydroxydiphenylmethane,1,1-bis(4-hydroxyphenyl)cyclohexane,1,1-bis(4-hydroxy-3-methylphenyl)cyclohexane,4,4′-(1-α-methylbenzylidene)bisphenol,1,3-bis[2-(4-hydroxyphenyl)-2-propyl]benzene,α,α′-bis(4-hydroxyphenyl)-1,4-diisopropylbenzene,α,α′-bis(4-hydroxy-3,5-dimethylphenyl)-1,4-diisopropylbenzene,9,9-bis(4-hydroxyphenyl)fluorene,9,9-bis(4-hydroxy-3-methylphenyl)fluorene, 4,4′-dihydroxybenzophenone,bis(4-hydroxyphenyl)sulfone, bis(4-hydroxy-3,5-dimethylphenyl)sulfone,octafluoro-4,4′-biphenol, bis(4-fluorophenyl)sulfone, and2,2-bis(4-hydroxyphenyl)hexafluoropropane.

Examples of the aromatic disulfide used for the synthesis of aromaticpolysulfide include p-benzenedithiol, m-benzenedithiol,4,4′-oxybisbenzenethiol, 4,4′-thiobisbenzenethiol, and4,4′-biphenyldithiol.

Examples of the aromatic dihalide used for the synthesis of aromaticpolyether or aromatic polysulfide include 4,4′-dichlorobenzophenone,4,4′-difluorobenzophenone, 4,4′-dichlorophenyl sulfone,bis(4-fluorophenyl)sulfone, bis(4-fluoro-3-nitrophenyl)sulfone,2,6-dichlorobenzonitrile, 2,6-difluorobenzonitrile,2,4-difluorobenzonitrile, tetrafluoroisophthalonitrile,perfluorobiphenyl, and 3,5-dichloro-1-methoxytriazine. Further, insteadof dihalide, dinitro compounds such as 2,4-dinitrobenzonitrile and2,6-dinitrobenzonitrile may be used.

The aromatic polycarbonate is synthesized generally by a method ofallowing bisphenol to react with phosgene in a solution, or a method ofallowing bisphenol to react with a carbonate such as diphenyl carbonatein a melt state. By introducing one or a plurality of various kinds ofstructures into bisphenol, the refractive index can be changedarbitrarily from 1.5 to 1.65.

As bisphenol used for synthesizing aromatic polycarbonate, bisphenolused for synthesizing the above aromatic polyether is used.

In addition to the above bisphenol or aromatic disulfide, aliphatic dioland aliphatic disulfide can be used together with aromatic polyether,aromatic polysulfide, and aromatic polycarbonate.

Further, it is more preferred that a compound having one or moreo-hydroxyphenoxypropylsiloxy groups be substituted for a part ofbisphenol or aromatic disulfide. According to this method, a(—SiR₂—O—)_(n) group can be introduced into a resin, whereby theadherence with respect to a substrate is enhanced.

It is preferred that the refractive index ni of the layer 29 containingan organic resin as a main component of the present invention satisfynb≧ni≧ns with respect to the refractive index nb of the substrate 25 andthe refractive index ns of the plate crystal layer 30 formed of platecrystal containing the aluminum oxide as a main component. It ispreferred to select an organic resin or a structure in the organic resinas such. By adjusting ni in this range, a high antireflection propertycan be exhibited.

Further, the layer 29 containing an organic resin as a main componentcan contain a silane coupling agent in addition to the organic resin sothat adherence can be enhanced. Further, in order to adjust therefractive index and decrease the percentage of water absorption,inorganic fine particles such as SiO₂, TiO₂, ZrO₂, SiO₂, ZnO, MgO, andAl₂O₃ can be mixed in a small amount. The amount of components otherthan the organic resin, which can be mixed, is less than 20 parts byweight based on 100 parts by weight of the entire organic resin layer,and when the components are mixed in an amount exceeding 20 parts byweight, there is a possibility that transparency and uniformity of afilm thickness may be impaired.

It is easy to apply the organic resin to a substrate as a solution,which is preferred because this method is suitable for forming a thinfilm. In the case of a cured resin, a reactive or polymerizable compoundor oligomer can be used by dissolving them in an organic solventtogether with an initiator and a curing agent. On the other hand, athermoplastic resin can be used by dissolving it in an organic solventalone or together with a component other than an organic resin. In thecase where the thermoplastic resin itself is insoluble or difficult tobe solved in an organic solvent, a thermoplastic resin precursor can beused by dissolving it in an organic solvent. In the case of the latter,the process of converting the precursor into a thermoplastic resin isrequired.

Examples of an organic solvent used for forming the layer 29 containingan organic resin as a main component of the present invention include:ketones such as 2-butanone, methylisobutyl ketone, cyclopentanone, andcyclohexanone; esters such as ethyl acetate, n-butyl acetate,ethyleneglycol monomethylether acetate, propyleneglycol monomethyletheracetate, and ethyl lactate; ethers such as tetrahydrofuran, dioxane, anddiisopropyl ether; various aromatic hydrocarbons such as toluene,xylene, and ethylbenzene; chlorinated hydrocarbons such as chloroform,methylene chloride, and tetrachloroethane; and solvents such asN-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide,dimethyl sulfoxide, and sulfolane. Further, alcohols such as 1-butanol,methyl cellosolve, diglime, and methoxypropanol may also be used.

As the method of forming the layer 29 containing an organic resin as amain component using a solution of an organic resin, known coating meanscan be appropriately used, such as dipping, spin coating, spraying,printing, flow coating, and a combination thereof.

After coating of an organic resin solution, it is preferred to heat thesolution at 60° C. to 240° C. for 5 minutes to 2 hours so as to removethe solvent. In the case of a resin curable with heat, the removal ofthe solvent and the curing of the resin can be performed simultaneouslyby this heat treatment. On the other hand, in the case of a resincurable with another means other than heat, it is necessary toappropriately select the irradiation of light such as UV-light, a laser,an electron beam, an X-ray, and a microwave, a radiation or anelectromagnetic wave. Even in the case of curing a resin with anothermeans other than heat, the reaction can be promoted by conductingfurther heat treatment.

The thickness of the layer 29 of the present invention containing anorganic resin as a main component is 10 nm or more and 150 nm or less,more preferably 20 nm or more and 100 nm or less. If the thickness isless than the range, it is difficult to form a uniform coating, anddesirable optical characteristics cannot be obtained. If the thicknessis greater than the range, contribution to the reflection reducingeffect is reduced due to interference and the like.

Substrates to be used in the present invention include glass, resins,glass mirrors and mirrors formed of resin. Typical examples of resinsubstrate include films and molded products of thermoplastic resins,such as polyester, triacetyl cellulose, cellulose acetate, polyethyleneterephthalate, polypropylene, polystyrene, polycarbonate, polysulfone,polyacrylate, polymethacrylate, an ABS resin, polyphenylene oxide,polyurethane, polyethylene, polycycloolefin, and polyvinyl chloride;cross-linked films and cross-linked molded products obtained fromvarious kinds of thermosetting resins, such as an unsaturated polyesterresin, a phenol resin, a cross-linked polyurethane, a cross-linked acrylresin, and a cross-linked saturated polyester resin. Specific examplesof glass may include no alkali glass and alumina silicate glass.Substrates for use in the present invention, which may be formed of anymaterials capable of being finally formed into a shape according to ause purpose, include flat plates, films, and sheets, and may have atwo-dimensional or three-dimensional curved surface. The thickness canbe appropriately determined, and is generally 5 nm or less, but is notlimited thereto.

The optical transparent element of the present invention may be furtherprovided with a layer for imparting various kinds of functions, inaddition to the layers described above. For example, a hard coat layermay be provided on the layer of plate crystals for improving thehardness of the film, or a water-repellent layer of fluoroalkyl silaneor alkyl silane may be provided for imparting water repellency. For thepurpose of preventing deposition of contaminants, or the like, a layerof a material having a refractive index lower than that of platecrystals containing aluminum oxide as a main component, or a layerformed of an amphipathic compound may be provided. For improving theadherence between the substrate and the layer containing an organicresin as a main component, an adhesive layer or a primer layer may beused.

EXAMPLES

Hereinafter, the present invention will be described specifically withexamples. However, the present invention is not limited to the examples.Optical films obtained in examples and comparative examples and havingfine unevenness on the surface were evaluated by the methods describedbelow.

Synthesis of Polyimides 1 to 5

Diamine (1), diamine (2), and diamine (3) in an amount of 0.012 mol intotal were dissolved in N,N-dimethylacetamide (hereinafter, abbreviatedas DMAc). While the diamine solution was cooled with water, 0.12 mol ofacid dianhydride was added thereto. The amount of DMAc was set so thatthe total mass of diamine and acid dianhydride became 20% by weight. Thesolution was stirred at room temperature for 15 hours, whereby apolymerization reaction was performed. After the solution was dilutedwith DMAc so as to be 8% by weight, and 7.4 ml of pyridine and 3.8 ml ofacetic anhydride were added to the resultant solution, followed bystirring at room temperature for 1 hour. Further, the solution wasstirred for 5 hours while it was heated to 50° C. in an oil bath. Thepolymerized solution was re-precipitated in methanol to extract apolymer, and thereafter, washed in methanol several times. After thesolution was dried in vacuum at 100° C., a light yellow powderypolyimide was obtained. The remaining amount of a carboxyl group wasmeasured from a ¹H-NMR spectrum to obtain the imidization rate. Table 1shows compositions of polyimides 1 to 5.

TABLE 1 Imidi- zation Diamine Diamine Diamine rate Anhydride (1) (2) (3)(%) Polyimide TDA-100 BAPB (0.9) BAPS (0.1) — 98 1 Polyimide TDA-100BAPP (0.9) LS- — 98 2 7430 (0.1) Polyimide TDA-100 m-TB (0.9) DADCM(0.4) LS- 96 3 7430 (0.1) Polyimide TDA-100 DADCM (0.9) LS- — 95 4 7430(0.1) Polyimide 6FDA DADCM (0.9) LS- — 98 5 7430 (0.1) TDA-100:4-(2,5-dioxotetrahydrofuran-3-yl)-1,2,3,4-tetrahydronaphthalene-1,2-dicarboxylicanhydride 6FDA: 4,4′-(hexafluoroisopropylidene)diphtalic dianhydrideBAPB: 4,4′-bis(4-aminophenoxy)biphenyl BAPP:2,2-bis[4-(4-aminophenoxy)phenyl]propane DADCM:4,4′-diaminodicyclohexylmethane LS-7430:1,3-bis(3-aminopropyl)tetramethyldisiloxane

(2) Synthesis of Polyether Ether Ketone 6

2.18 g of 4,4′-difluorobenzophenone, 3.79 g of9,9-bis(4-hydroxy-3-methylphenyl)fluorene, and 1.72 g of potassiumcarbonate were added to 15 ml of DMAc, and stirred at room temperature.Further, 7.5 ml of toluene was added to the mixture, and moisture in thesystem was azeotropically removed while being heated to 120° C. Thetemperature was raised to 150° C., whereby toluene was removedcompletely. Further, the temperature was raised to 165° C., andpolymerization was performed for 8 hours. After the mixture was dilutedwith 15 ml of DMAc, the polymerized solution was poured to acidicmethanol to obtain a white fibrous polymer. The polymer was washedrepeatedly with methanol, followed by drying, whereby polyether etherketone 6 was obtained with a yield of 95%.

(3) Preparation of Polyimide Solutions 6 to 10

2.5 g powder of polyimides 1 to 5 was dissolved in cyclohexanone toprepare polyimide solutions 6 to 10.

(4) Preparation of Polycarbonate Solution 11

2.5 g of bisphenol Z polycarbonate (Z-400 (Trade Name) manufactured byMitsubishi Gas Chemical Company, Inc.) was dissolved in cyclohexanone toprepare polycarbonate solution 11.

(5) Preparation of Thermosetting Resin Solution 12

5 g of melamine resin (NIKALAC MX-750LM (Trade Name) manufactured byNippon Carbide Industries Co., Inc.) and 0.025 g of p-toluene sulfonicacid were dissolved in 95 g of 1-methoxy-2-propanol to preparethermosetting resin solution 12.

(6) Preparation of SiO₂—TiO₂ Sol Solution 13

A mixed solvent of 3.15 g of 0.01 M diluted hydrochloric acid [HClaq.]and 29.5 g of 1-butanol/2-propanol (hereinafter, abbreviated as IPA) ata ratio of 1/1 (wt.) was added slowly to 14.6 g of ethyl silicate, andstirred at room temperature. After stirring for 6 hours, the resultantmixture was diluted with 92.5 g of a mixed solvent of 1-butanol/IPA at aratio of 1/1 (wt.) to obtain an A-solution. Then, 10.2 g of tetran-butoxytitanate and 3.9 g of ethylacetacetate were successivelydissolved in 25.5 g of the mixed solvent of 1-butanol/IPA at a ratio of1/1 (wt.). This solution was stirred at room temperature for 3 hours toobtain a B-solution. While the A-solution was being stirred, theB-solution was added thereto slowly, and the mixture was stirred forfurther 3 hours at room temperature, whereby a SiO₂—TiO₂ sol solution 13with a Si/Ti molar ratio of 7/3 was prepared.

(7) Preparation of Aluminum Oxide (Alumina(Al₂O₃)) Sol Solution 14

24.6 g of Al(O-sec-Bu)₃ was dissolved in 115.3 g of a mixed solvent of1-butanol/2-propanol (hereinafter, abbreviated as IPA) at a ratio of 1/1(wt.), and 6.51 g of 3-ethyl oxybutanoate was added to the mixture,followed by stirring at room temperature for about 1 hour. After that,0.01 M diluted hydrochloric acid [HClaq.] was added to the solution, andstirred at room temperature for about 3 hours. Further, the solution wasstirred in an oil bath at 120° C. for 6 hours, whereby an alumina(Al₂O₃) sol solution 13 was prepared.

(8) Preparation of Aluminum Oxide (Alumina(Al₂O₃) Sol Solution 15

17.2 g of Al(O-sec-Bu)₃ was dissolved in 122.3 g of a mixed solvent of1-butanol/2-propanol (hereinafter, abbreviated as IPA) at a ratio of 1/1(wt.), and 4.56 g of 3-ethyl oxybutanoate was added to the solution,followed by stirring at room temperature for about 1 hour. After that,0.01 M diluted hydrochloric acid [HClaq.] was added to the solution, andstirred at room temperature for about 3 hours. Further, the solution wasstirred in an oil bath at 120° C. for 6 hours, whereby an alumina(Al₂O₃) sol solution 14 was prepared.

(9) Preparation of a Silane Coupling Agent Solution 16

0.5 g of 3-aminopropylethoxysilane was dissolved in 99.5 g of ethanol,and 0.5 g of ion exchange water was further added to the resultantsolution. The solution was stirred at room temperature overnight toobtain a silane coupling agent solution 15.

(10) Preparation of Polyether Ether Ketone Solution 17

2.5 g of powder of polyether ether ketone 6 was dissolved in 10 g ofcyclohexanone to prepare a polyether ether ketone solution 17.

(11) Preparation of a Polysulfone Solution 18

2.5 g of pellet-shaped polysulfone (Mn of 16,000 or more, manufacturedby Sigma-Aldrich Corp.) was dissolved in 10 g of γ-butyrolactone toprepare a polysulfone solution 18.

(12) Preparation of a Polystyrene Solution 19

2.5 g of powder of polystyrene (manufactured by Sigma-Aldrich Corp.) wasdissolved in 10 g of cyclohexanone to prepare a polystyrene solution 19.

(13) Measurement of Percentage of Water Absorption of an Organic Resin

A coating film of various kinds of organic resins was formed on asilicon substrate and sintered at 200° C. for 60 minutes. After that,the water absorption amount of the film after being soaked inion-exchanged water at 23° C. for 24 hours was measured with athermogravimetric apparatus (TG/TDA, Thermo plus 2 manufactured byRigaku Corporation) to obtain the water absorption ratio of the film.

(14) Washing of Substrate

Various kinds of glass substrates with a size of about φ30 mm and athickness of about 2 mm with both surfaces polished were subjected toultrasonic washing with an alkali detergent and IPA, and dried in anoven.

(15) Observation of Shape of Coating

The surface of a surface layer of a coating was photographicallyobserved (acceleration voltage; 10.0 kV, magnification; 30,000) using ascanning electron microscope (FE-SEM, 54500 manufactured by HitachiLtd.).

(16) Measurement of Transmittance

A transmittance was measured over a range of 350 nm to 850 nm using anautomatic optical member measuring apparatus (V-570 manufactured byJASCO). A disc glass plate was used. The angle of incidence of light inmeasurements of transmittance was 0°.

(17) Measurement of Film Thickness and Refractive Index

Measurements were made over a range of wavelengths from 380 nm to 800 nmby a spectral ellipsometer (VASE manufactured by J. A. Woollam JAPANCo., Inc.).

Example 1

An appropriate amount of the polyimide solution 6 was dropped onto onesurface of the S-TIH53 (n_(550nm)=1.84) substrate washed by the abovemethod, followed by spin coating at 3,000 rpm for 20 seconds. Thesubstrate was pre-dried at 80° C. for 10 minutes, and thereafter, theother surface was similarly spin-coated with the polyimide solution 6.After that, the resultant substrate was sintered in a hot aircirculation oven at 200° C. for 30 minutes, whereby a substrate with anorganic resin layer having the polyimide 1 on both surfaces wasproduced. Table 2 shows the thickness, refractive index, and percentageof water absorption of the polyimide film 1.

An appropriate amount of an alumina sol solution 14 was dropped onto onesurface of the substrate with the film of the polyimide 1, followed byspin coating at 4,000 rpm for 20 seconds and pre-drying at 80° C. for 10minutes. The other surface was similarly spin coated with the aluminasol solution. After that, the resultant substrate was sintered in a hotair circulation oven at 200° C. for 30 minutes, whereby the substratewas covered with transparent amorphous Al₂O₃ films.

Next, the substrate was soaked in hot water at 80° C. for 30 minutes,and dried at 60° C. for 10 minutes.

The surface of the obtained film was observed by the FE-SEM to find afine uneven structure in which plate crystals containing Al₂O₃ as a maincomponent were tangled randomly and complicatedly as shown in FIG. 4. Bythe observation of the cross-section by the FE-SEM, it was observed thata plate crystal layer containing Al₂O₃ as a main component was arrangedselectively with an average angle of 75° with respect to the surface ofthe substrate.

Then, for the obtained film, the film thickness and the refractive indexwere measured using ellipsometry. The thickness and the refractive indexof each film are shown in Table 3.

For this substrate, a high-temperature and high-humidity test at atemperature of 60° C. and a humidity of 90% was conducted as anaccelerated test for examination on durability of optical performance,and the transmittance was measured at the start, after 250 hours andafter 500 hours. The results thereof are shown in Table 3.

Example 2

The same operation as in Example 1 was conducted except for using thepolyimide solution 7 in place of the polyimide solution 6 to form anorganic resin layer formed of the polyimide 2.

Example 3

The same operation as in Example 2 was conducted except for replacingthe substrate by S-LAH65 (n_(550nm)=1.80).

Example 4

The same operation as in Example 3 was conducted except for using thepolyimide solution 8 in place of the polyimide solution 7 to form anorganic resin layer formed of the polyimide 3.

Example 5

The same operation as in Example 3 was conducted except for using thepolyimide solution 9 in place of the polyimide solution 7 to form anorganic resin layer formed of the polyimide 4.

Example 6

An appropriate amount of the silane coupling agent solution 16 wasdropped onto one surface of the washed S-LAH65 (n_(550nm)=1.80)substrate, followed by spin coating at 4,000 rpm for 20 seconds. Theresultant substrate was dried at 80° C. for 10 minutes, and the othersurface was similarly spin-coated with the silane coupling agentsolution 16, followed by sintering at 80° C. for 10 minutes. Anappropriate amount of the polycarbonate solution 11 was dropped onto onesurface of the substrate, followed by spin coating at 3,000 rpm for 20seconds. The resultant substrate was pre-dried at 80° C. for 10 minutes,and thereafter the other surface was similarly spin-coated with thepolycarbonate solution 11. The resultant substrate was sintered in a hotair circulation oven at 200° C. for 60 minutes, whereby a substrate withan organic resin layer formed of bisphenol Z polycarbonate was produced.Table 2 shows the film thickness, refractive index, and percentage ofwater absorption of the thermosetting resin film.

Hereinafter, a transparent amorphous Al₂O₃ film was coated in the sameway as in Example 1, and evaluated.

Example 7

The same operation as in Example 6 was conducted except for using thethermosetting resin solution 12 in place of the polycarbonate solution11 to form an organic resin layer formed of a thermosetting resin.

Example 8

The same operation as in Example 4 was conducted except for replacingthe substrate by S-LAH66 (n_(550nm)=1.77).

Example 9

The same operation as in Example 8 was conducted except for using thepolyimide solution 9 in place of the polyimide solution 8 to form theorganic resin layer formed of the polyimide 4.

Example 10

The same operation as in Example 6 was conducted except for replacingthe substrate by S-LAH66 (n_(550nm)=1.77).

Example 11

The same operation as in Example 7 was conducted except for replacingthe substrate by S-LAH66 (n_(550nm)=1.77).

Example 12

The same operation as in Example 1 was conducted except for replacingthe substrate by S-TIH1 (n_(550nm)=1.71) and using the polyimidesolution 10 in place of the polyimide solution 6 to form an organicresin layer formed of the polyimide 5.

Example 13

The same operation as in Example 6 was conducted except for replacingthe substrate by S-TIH1 (n_(550nm)=1.71).

Example 14

An appropriate amount of the polyimide solution was dropped onto onesurface of the washed S-LAH65 (n_(550nm)=1.80) substrate, followed byspin coating at 3,000 rpm for 20 seconds. The substrate was pre-dried at80° C. for 10 minutes, and thereafter, the other surface was similarlyspin-coated with the polyimide solution 7. After that, the resultantsubstrate was sintered in a hot air circulation oven at 200° C. for 30minutes, whereby a substrate with an organic resin layer having thepolyimide 2 on both surfaces was produced.

An appropriate amount of an alumina sol solution 15 was dropped onto onesurface of the substrate with the film of the polyimide 2, followed byspin coating at 2,700 rpm for 20 seconds and pre-drying at 80° C. for 10minutes. The other surface was similarly spin coated with the aluminasol solution 15. After that, the resultant substrate was sintered in ahot air circulation oven at 200° C. for 10 minutes. Further, bothsurfaces were coated again with the alumina sol solution 15 by the samemethod, and the substrate was finally sintered at 200° C. for 30minutes, whereby the substrate was covered with transparent amorphousAl₂O₃ films.

Next, the substrate was soaked in hot water at 80° C. for 30 minutes,and dried at 60° C. for 10 minutes.

Hereinafter, the same evaluation as that in Example 1 was conducted.

Example 15

The same operation as in Example 14 was conducted except for using thepolycarbonate solution 11 in place of the polyimide solution 9 to forman organic resin layer formed of polycarbonate.

Example 16

The same operation as in Example 6 was conducted except for using thepolyether ether ketone solution 17 in place of the polycarbonatesolution 11 to form an organic resin layer formed of polyether etherketone.

Example 17

The same operation as in Example 6 was conducted except for using thepolysulfone solution 18 in place of the polycarbonate solution 11 toform an organic resin layer formed of polysulfone.

Comparative Example 1

An appropriate amount of the alumina sol solution 14 was dropped ontoone surface of the washed S-TIH53 (n_(550nm)=1.84) substrate, followedby spin coating at 4,000 rpm for 20 seconds and pre-drying at 80° C. for10 minutes. The other surface was similarly spin coated with the aluminasol solution. After that, the resultant substrate was sintered in a hotair circulation oven at 200° C. for 30 minutes, whereby the substratewas covered with transparent amorphous Al₂O₃ films.

Next, the substrate was soaked in hot water at 80° C. for 30 minutes,and dried at 60° C. for 10 minutes.

Hereinafter, the same evaluation as that in Example 1 was conducted.

Comparative Example 2

The same operation as that in Comparative Example 1 was conducted exceptfor replacing the substrate by S-LAH65 (n_(550nm)=1.80).

Comparative Example 3

An appropriate amount of the SiO₂—TiO₂ sol solution 13 was dropped ontoone surface of the washed S-TIH53 (n_(550nm)=1.84) substrate, followedby spin coating at 3,000 rpm for 20 seconds. After the substrate waspre-dried at 80° C. for 10 minutes, the other surface was similarlyspin-coated with the SiO₂—TiO₂ sol solution 13. After that, thesubstrate was sintered in a hot air circulation oven at 200° C. for 60minutes, whereby the substrate with amorphous SiO₂—TiO₂ films on bothsurfaces was produced. Table 2 shows the film thickness, refractiveindex, and percentage of water absorption of the amorphous SiO₂—TiO₂film.

Hereinafter, an antireflection film was formed by the same method asthat in Example 1 after covering the substrate with the amorphous Al₂O₃films, and evaluation was conducted.

Comparative Example 4

The same operation as that in Comparative Example 3 was conducted exceptfor replacing the substrate by S-LAH65 (n_(550nm)=1.80).

Comparative Example 5

The same operation as in Example 6 was conducted except for using thepolystyrene solution 19 in place of the polycarbonate solution 11 toform an organic resin layer formed of polystyrene. However, when thesubstrate was soaked in hot water after being covered with the amorphousAl₂O₃ films, film peeling occurred from an organic intermediate layer,with the result that an antireflection film was not obtained.

TABLE 2 Percentage of water Solution absorption (%) Polyimide 1Polyimide solution 6 1.2 Polyimide 2 Polyimide solution 7 1.3 Polyimide3 Polyimide solution 8 0.8 Polyimide 4 Polyimide solution 9 1.8Polyimide 5 Polyimide solution 10 0.6 Bisphenol z Polycarbonate solution11 0.2 polycarbonate Thermosetting Thermosetting resin 0.8 resinsolution 12 Polyether ether Polyether ether ketone 0.2 ketone solution17 Polysulfone Polysulfone solution 18 0.3 Polystyrene Polystyrenesolution 19 0.1 (Note) Percentage of water absorption: after soaking inion exchanged water at 23° C. for 24 hours

TABLE 3 Plate crystal layer containing Al₂O₃ Transmittance measurementSubstrate Organic resin layer as a main component result (550 nm) high-Refractive Film Refractive Film Refractive temperature and high-humiditytest Kind index Kind thickness index thickness index At start 250 hours500 hours Example 1 S-TIH53 1.84 Polyimide 1 78 1.66 250 1.42-1.0 99.399.2 99.2 Example 2 S-TIH53 1.84 Polyimide 2 75 1.63 250 1.42-1.0 99.299.1 99.0 Example 3 S-LAH65 1.80 Polyimide 2 75 1.63 250 1.42-1.0 99.299.2 99.2 Example 4 S-LAH65 1.80 Polyimide 3 79 1.61 250 1.42-1.0 99.499.5 99.4 Example 5 S-LAH65 1.80 Polyimide 4 78 1.57 250 1.43-1.0 99.499.3 99.2 Example 6 S-LAH65 1.80 Polycarbonate 80 1.59 250 1.43-1.0 99.399.3 99.2 Example 7 S-LAH65 1.80 Thermosetting resin 70 1.61 2501.42-1.0 99.2 99.2 99.0 Example 8 S-LAH66 1.77 Polyimide 3 79 1.61 2501.42-1.0 99.4 99.5 99.4 Example 9 S-LAH66 1.77 Polyimide 4 78 1.57 2501.42-1.0 99.5 99.5 99.4 Example 10 S-LAH66 1.77 Polycarbonate 80 1.59250 1.42-1.0 99.5 99.4 99.4 Example 11 S-LAH66 1.77 Thermosetting resin70 1.61 250 1.42-1.0 99.4 99.3 99.1 Example 12 S-TIH1 1.71 Polyimide 578 1.56 250 1.43-1.0 99.4 99.3 99.3 Example 13 S-TIH1 1.71 Polycarbonate80 1.59 250 1.42-1.0 99.5 99.4 99.3 Example 14 S-LAH65 1.80 Polyimide 275 1.63 200 1.42-1.0 99.2 99.1 99.1 Example 15 S-LAH65 1.80Polycarbonate 80 1.59 200 1.42-1.0 99.2 99.2 99.1 Example 16 S-LAH651.80 Polyether ether ketone 75 1.62 250 1.42-1.0 99.5 99.4 99.3 Example14 S-LAH65 1.80 Polysulfone 78 1.63 200 1.42-1.0 99.2 99.1 99.0Comparative S-TIH53 1.84 — — — 250 1.40-1.0 97.5 94.2 90.0 Example 1Comparative S-LAH65 1.80 — — — 250 1.40-1.0 98.0 95.4 93.3 Example 2Comparative S-TIH53 1.84 SiO₂—TiO₂ 85 1.61 250 1.40-1.0 99.2 98.2 94.2Example 3 Comparative S-LAH65 1.80 SiO2—TiO2 85 1.61 250 1.40-1.0 99.497.8 93.5 Example 4 Comparative S-LAH65 1.80 Polystyrene 70 1.59 Peelingfrom intermediate layer during hot water treatment Example 5 (Note) Therefractive index of the crystal layer of plate crystals shows values ofa starting point and an ending point of an inclination refractive indexpart. For example, the refractive index 1.42-1.0 in Example 1 shows thatthe refractive index continuously decreases from 1.42 to 1.0.

Performance Evaluation

As a result of comparing the transmittance at 550 nm with respect to theproduced optical films, optical members were obtained with which a hightransmittance was kept even after an acceleration durability test inhigh temperature and high humidity in Examples 1 to 17. On the otherhand, in Comparative Example 5, an antireflection film capable of beingevaluated for the performance was not obtained due to film peeling. InComparative Examples 1 and 2, the transmittance was low from thebeginning, and the transmittance was decreased after the accelerationdurability test in Comparative Examples 3 and 4.

Example 18

FIG. 6 is a front view of an optical member of Example 16. In thisfigure, an optical member 1 is a concave lens, and a substrate 2 isprovided with an optical member 3.

FIG. 7 illustrates a cross-section of the optical member of Example 18cut taken along the 7-7 section in FIG. 6. A layer containing an organicresin as a main component, and a layer having arranged plate crystalscontaining aluminum oxide as a main component are formed on an opticalsurface, and an optical member 3 having an uneven profile is formed onthe outermost surface, whereby reflection of light at the opticalsurface is reduced.

In this example, the optical member is a concave lens, but the presentinvention is not limited thereto, and the lens may be either a convexlens or a meniscus lens.

Example 19

FIG. 8 is a front view of an optical member of Example 19. In thisfigure, an optical member 1 is a prism, and a base body 2 is providedwith an optical member 3.

FIG. 9 shows a cross-section of the optical member of Example 19 cuttaken along the 9-9 section in FIG. 8. A layer containing an organicresin as a main component, and a layer having arranged plate crystalscontaining aluminum oxide as a main component are formed on an opticalsurface, and the optical member 3 having an uneven profile is formed onthe outermost surface, whereby reflection of light at the opticalsurface is reduced.

In this example, angles formed by optical surfaces of the prism are 90°C. and 45° C., but the present invention is not limited thereto, and theoptical surfaces of the prism may form any angle.

Example 20

FIG. 10 is a front view of an optical member of Example 20 of thepresent invention. In this figure, an optical member 1 is a fly eyeintegrator, and a substrate 2 is provided with an optical member 3.

FIG. 11 shows a cross-section of an optical member of Example 20 cuttaken along the 11-11 section in FIG. 10. A layer containing an organicresin as a main component, and a layer having arranged plate crystalscontaining aluminum oxide as a main component are formed on an opticalsurface, and an optical member 3 having an uneven profile is formed onthe outermost surface, whereby reflection of light at the opticalsurface is reduced.

Example 21

FIG. 12 is a front view of an optical member of Example 21 of thepresent invention. In this figure, an optical member 1 is an fθ lens,and a substrate 2 is provided with an optical member 3.

FIG. 13 illustrates a cross-section of an optical member of Example 21cut taken along the 13-13 section in FIG. 12. A layer containing anorganic resin as a main component, and a layer having arranged platecrystals containing aluminum oxide as a main component are formed on anoptical surface, an the optical member 3 having an uneven profile isformed on the outermost surface, whereby reflection of light at theoptical surface is reduced.

Example 22

An example in which the optical member of the present invention is usedin an observation optical system is shown as Example 22 of the presentinvention. FIG. 14 illustrates a cross-section of one of a pair ofoptical systems of a binocular.

In this figure, reference numeral 4 denotes an objective lens, referencenumeral 5 denotes a prism (shown in an exposed form) for inverting animages reference numeral 6 denotes an eye lens, reference numeral 7denotes an image formation surface, and reference numeral 8 denotes apupil surface (evaluation surface). In the figure reference numeral 3(shown with a legend) denotes an optical transparent element relating tothe present invention. A layer containing an organic resin as a maincomponent, and a layer having arranged plate crystals containingaluminum oxide as a main component are formed, and the outermost surfacehas an uneven profile, whereby reflection of light at each opticalsurface is reduced. In this example, the optical member 3 formed of afine uneven configuration is provided neither on an optical surface 9 ofthe objective lens closest to an object nor on an optical surface 10 ofthe eye lens closest to the evaluation surface. The reason why theoptical member 3 is not provided on these surfaces is that itsperformance will be degraded due to contact while it is used, but thepresent invention is not limited thereto, and the optical member 3 maybe provided on the optical surfaces 9 and 10.

Example 23

An example in which the optical member of the present invention is usedin an imaging optical system is shown as Example 23 of the presentinvention. FIG. 15 illustrates a cross-section of a photographing lens(telephoto lens is illustrated in this figure) of a camera or the like.

In this figure, reference numeral 7 denotes a film as an image formationsurface, or a solid imaging device (photoelectric conversion element)such as a CCD or a CMOS, and reference numeral 11 denotes a diaphragm.In the figure, reference numeral 3 (shown with a legend) denotes anoptical member relating to the present invention. A layer containing anorganic resin as a main component, and a layer having arranged platecrystals containing aluminum oxide as a main component are formed, andthe outermost surface has an uneven profile, whereby reflection of lightat each optical surface is reduced. In this example, the optical member3 formed of a fine uneven configuration is not provided on an opticalsurface 9 of the objective lens closest to an object. The reason why theoptical member 3 is not provided on the surface is that its performancewill be degraded due to contact while it is used, but the presentinvention is not limited thereto, and the optical member 3 may beprovided on the optical surface 9.

Example 24

An example in which the optical member of the present invention is usedin a projection optical system (projector) is shown as Example 24 of thepresent invention. FIG. 16 illustrates a cross-section of a projectoroptical system.

In this figure, reference numeral 12 denotes a light source, referencenumerals 13 a and 13 b denote fly eye integrators, reference numeral 14denotes a polarizing conversion element, reference numeral 15 denotes acondenser lens, reference numeral 16 denotes a mirror, reference numeral17 denotes a field lens, reference numerals 18 a, 18 b, 18 c and 18 ddenote prisms, reference numerals 19 a, 19 b and 19 c denote lightmodulation elements, and reference numeral 20 denotes a projection lens.In the figure, reference numeral 3 (shown with a legend) denotes anoptical transparent element relating to the present invention. A layercontaining an organic resin as a main component, and a layer havingarranged plate crystals containing aluminum oxide as a main componentare formed, and the outermost surface has an uneven profile, wherebyreflection of light at each optical surface is reduced.

Because the optical member 3 of this example is configured to contain aninorganic component such as silica or alumina as a main component, theoptical member 3 has a high heat resistance, and never suffers from adegradation in performance even if placed at a position 13 a so close tothe light source 12 that the optical member 3 is exposed to high heat.

Example 25

An example in which the optical member of the present invention is usedin a scan optical system (laser beam printer) is shown as Example 25 ofthe present invention. FIG. 17 illustrates a cross-section of a scanoptical system.

In this figure, reference numeral 12 denotes a light source, referencenumeral 21 denotes a collimator lens, reference numeral 11 denotes anaperture diaphragm, reference numeral 22 denotes a cylindrical lens,reference numeral 23 denotes a light deflector, reference numerals 24 aand 24 b denote fθ lenses, and reference numeral 7 denotes an imagesurface. In the figure, reference numeral 3 (shown with a legend)denotes an optical transparent element relating to the presentinvention. A layer containing an organic resin as a main component, anda layer having arranged plate crystals containing aluminum oxide as amain component are formed, and the outermost surface has an unevenprofile, whereby reflection of light at each optical surface is reducedto realize formation of high-quality images.

The optical member of the present invention can be adapted to atransparent substrate having any refractive index, shows an excellentantireflection effect to visible light, and has a long-term weatherresistance, and therefore it can be used for various kinds of displaysof word processors, computers, televisions, plasma display panels, andthe like; optical members such as polarizing plates of liquid crystalapparatuses, sunglass lenses, graduated eyeglass lenses, finder lensesfor cameras, prisms, fly-eye lenses, toric lenses, various kinds ofoptical filters, sensors and the like, which are formed of various kindsof optical glass materials and transparent plastics; and further,photographic optical systems using those optical members, observationoptical systems such as binoculars, projection optical systems for usein liquid crystal projectors, various optical lenses of scan opticalsystems for use in laser printers and the like, covers of various kindsof instruments, and window glasses of automobiles, electric trains, andthe like.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2007-040003, filed Feb. 20, 2007, and Japanese Patent Application No.2008-033290, filed Feb. 14, 2008 which are hereby incorporated byreference herein in their entirety.

What is claimed is:
 1. A method of manufacturing an optical member, the method comprising: forming a layer containing an organic resin as a main component on a substrate by applying to the substrate a solution containing the organic resin, the organic resin having an aromatic ring and/or an imide ring in a main chain; forming a layer containing aluminum oxide as a main component on the layer containing the organic resin; and subjecting the layer containing aluminum oxide as a main component to hot water treatment to form unevenness on a surface.
 2. The method of claim 1, wherein the step of subjecting the layer containing aluminum oxide as a main component to hot water treatment comprises a step of forming a crystal containing a hydroxide of aluminum or a hydrate of aluminum oxide.
 3. The method of claim 2, wherein the crystal containing a hydroxide of aluminum or a hydrate of aluminum oxide is boehmite.
 4. The method of claim 1, wherein the hot water treatment comprises soaking in hot water at 50° C. or higher or exposure to water vapor.
 5. The method of claim 1, wherein the refractive index nb of the substrate, the refractive index ni of the layer containing an organic resin as a main component, and the refractive index ns of the layer containing aluminum oxide as a main component after the hot water treatment satisfy nb≧ni≧ns.
 6. A method of manufacturing an optical member, the method comprising: forming a layer containing a polyimide as a main component on a substrate by applying to the substrate a solution containing the polyimide; forming a layer containing aluminum oxide as a main component on the layer containing the polyimide; and subjecting the layer containing aluminum oxide as a main component to hot water treatment to form unevenness on a surface.
 7. The method of claim 6, wherein the step of subjecting the layer containing aluminum oxide as a main component to hot water treatment comprises a step of forming a crystal containing a hydroxide of aluminum or a hydrate of aluminum oxide.
 8. The method of claim 7, wherein the crystal containing a hydroxide of aluminum or a hydrate of aluminum oxide is boehmite.
 9. The method of claim 6, wherein the hot water treatment comprises soaking in hot water at 50° C. or higher or exposure to water vapor.
 10. The method of claim 6, wherein the refractive index nb of the substrate, the refractive index ni of the layer containing an organic resin as a main component, and the refractive index ns of the layer containing aluminum oxide as a main component after the hot water treatment satisfy nb≧ni≧ns. 